One of a variety of external automotive lighting assemblies is generally characterized by two main parts including a molded opaque rear portion or housing and a permanently attached molded light-transmissive cover or lens. Depending upon the functional requirements such as for example a headlamp, the housing may include one or more reflectors such as by metalization of a parabolic or semi-parabolic surface. The housing further includes one or more bulb access apertures, typically keyed for twist-lock assembly of bulb and socket therethrough. Such lighting assemblies are typically sealed or substantially sealed with a certain degree of moisture permeability provided for by vapor membranes. In any case, a desired feature of such lighting assemblies is an impervious seal between the lens and housing and between the housing and bulb sockets. The latter is accomplished such as by conventional O-ring type seals. The former is accomplished generally by a sealing adhesive at the lens to housing interface.
Modern lighting designs are often driven by the styling and aerodynamic requirements which typically share the common objective of providing lighting assemblies which are flush with body panels. Such requirements often translate into lighting assemblies which wrap corners of the vehicle such as, for example, a combined headlight and side marker light assembly.
Often times the differences in material composition and or the geometric differences between a housing and a lens result in geometrical mismatch of the lens to housing interface due to creep of the parts away from the respective molded shapes as the parts cool or set. In a mass production environment, molded lenses and housings are desirably expeditiously moved through a series of stations including directly from mold to an assembly station whereat the lens and housing are joined by an adhesive. This undesirably may result in an unsealed assembly at one or more points about the interface of the lens and housing as creep sets in to the parts before the adhesive fully cures. Creeping of component parts may vary depending upon the materials and processes used in the manufacturing thereof and is generally due to material stresses introduced in the process and/or thereafter as the component part cools from a high process temperature. Therefore, for some time after the fabrication of component parts, it is common for the parts to relax into an equilibrium state or position which is dimensionally different from the process formed shape. Such component parts prior to substantial relaxation may be referred to as green parts or green components. Such relaxation phenomena generally are more prevalent in parts which turn a significant radius.
Proposals for addressing the general problems discussed herein include additional clamping of the lens and housing until the adhesive has attained a permanent set. Such solution is generally undesirable as additional manufacturing handling and complexity is introduced. Another proposed solution is to fixture the parts, again until such time as the adhesive sets. This too undesirably adds process handling and is extremely capital intensive requiring a multiplicity of fixturing apparatus. Another proposed solution is to drive anchor pins, screws or other intrusive fastener through the respective lens and housing material thus providing a mechanical fastening system between the two parts. This is generally undesirable in as much as such fasteners may require additional vehicle installation clearance, requires additional parts and handling and may be cosmetically unappealing.